Chap. VIII. SEXUAL SELECTION. 287 



and developed in the adult males alone. When, on the 

 other hand, the adult male closely resembles the young 

 of both sexes (these, with rare exceptions, being- alike), 

 he generally resembles the adult female ; and in most of 

 these cases the variations through which the young and 

 old acquired their present characters, probably occurred 

 in conformity with our rule during youth. But there is 

 here room for doubt, as characters are sometimes trans- 

 ferred to the offspring at an earlier age than that at 

 which they first appeared in the parents, so that the 

 parents may have varied w r hen adult, and have trans- 

 ferred their characters to their offspring whilst young. 

 There are, moreover, many animals, in which the two 

 sexes closely resemble each other, and yet both differ 

 from their young ; and here the characters of the adults 

 must have been acquired late in life ; nevertheless, 

 these characters in apparent contradiction to our rule, 

 are transferred to both sexes. We must not, however, 

 overlook the possibility or even probability of succes- 

 sive variations of the same nature sometimes occurring, 

 under exposure to similar conditions, simultaneously in 

 both sexes at a rather late period of life ; and in this case 

 the variations would be transferred to the offspring of 

 both sexes at a corresponding late age ; and there would 

 be no real contradiction to our rule of the variations 

 which occur late in life being transferred exclusively to 

 the sex in which they first appeared. This latter rule 

 seems to hold true more generally than the second rule, 

 namely, that variations which occur in either sex early 

 in life tend to be transferred to both sexes. As it was 

 obviously impossible even to estimate in how large a 

 number of cases throughout the animal kingdom these 

 two propositions hold good, it occurred to me to inves- 

 tigate some striking or crucial instances, and to rely 

 on the result. 



